RDMA/cma: Delete from restrack DB after successful destroy

Update the code to have similar destroy pattern like other IB objects.

This change create asymmetry to the rdma_id_private create flow to make
sure that memory is managed by restrack.

Link: https://lore.kernel.org/r/20200922091106.2152715-2-leon@kernel.org


Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>